Improvement in a plate bending process and related machine

Abstract: Process for bending a plate (1) of press-formable material, comprising the use of a blank-holder means (4) to firmly hold the plate on its horizontal plane between said blank-holder means and an appropriate anvil (2), and the subsequent actuation of a knife-shaped tool (11) to perform the bending operation, in which said actuation of said knife-shaped tool (11) consists of a first purely translational movement and a second purely rotational movement, wherein said first purely translational movement brings about a first bending by a 90°-angle of the edge portion of the plate to be bent, and said second purely rotational movement is effective in increasing the bending angle to any greater angle than 90°.

Description: This invention relates to a new sheet-metal bending process for metal plates, in particular to make bends with a greater angle than 90° in the butt-end or edge portion of sheet-metal plates with an elongated shape, as performed preferably by numerical-control (NC) presses, as well as the machines arranged to carry out such a process. Press-bending is a widely known technology in the sheet-metal forming industry, where it is used in much the same manner by the various manufacturers, except for some minor differences due mainly to various extents of automation implemented in the respective manufacturing processes. Such a technology is substantially based on the following fabrication cycle, which is briefly outlined below in order to facilitate a comparison with the cycle according to the present invention, which will be described further on. Essentially, the sheet-metal bending process is carried out in two distinct phases, which consist in Placing the sheet-metal plate to be folded on an appropriate anvil, which is generally known in the art by its name of 'dihedron' and is accordingly provided with an angled concavity, and in the downstroke of a plunger carrying, duly attached to its downward facing end, an appropriately shaped tool, which is generally known in the art by its name of 'knife'. In general, such an angled concavity of the dihedron and the knife are given such a shape that they are capable of fitting together perfectly. The progressively applied pressure of the knife against the sheet-metal plate, whereas the dihedron acts as an opposing and forming element, brings about the desired bending and plastic deformation effect in the sheet-metal plate while the latter is clamped by said elements, as anyone skilled in the art is well aware of. However, the use of this technique is limited to the bending of sheet-metal plates being quite small in their size. Actually, the following rule-of-thumb applies in general: the greater the bending angle, the smaller the size of the sheet-metal plate. The problems, therefore, arise when handling larger-sized sheet-metal plates and, particularly, when the need arises to bend beyond 90°, ie. creating 'undercuts', the butt-end or edge portions of elongated-shape sheet-metal plates, preferably by means of a single sheet-metal bending operation. Actually, it is theoretically possible to bend by such a large angle the butt-end or edge portion of a sheet-metal plate with a single sheet-metal bending operation. This, however, would require that the plate is not clamped in the process, but on the contrary stays free, and this would in turn bring about a number of undesired consequences. As a matter of fact, in such a case the penetration of the knife in the dihedron and the resulting deformation of the sheet-metal plate placed therebetween would cause the 'length' portion of the same plate, ie. the portion which is not actually involved by the bending process, to be rotated by an angle corresponding to the desired inclination of the bend. This has a number of unavoidable drawbacks as a consequence: on one hand, a great amount of raising motion by the rotation of the sheet-metal plate due to the sheet-metal bending operation is in general considered to be unacceptable owing to the really huge space requirements that this would imply, also in connection with the safety areas to be arranged therearound. On the other hand, if the sheet-metal plate is rather long, its raising may cause the plate to sag near the bending line owing to the flexural or bending load imposed by the weight of the raised portion of the sheet-metal plate. In practice, it is therefore not possible to obtain, by a single sheet-metal bending operation, the formation of a butt-end or edge bend in a sheet-metal plate with large bending angles, in particular with bending angles larger than 90° or undercuts, while keeping the plate in its horizontal position. From JP 59-33032 a bending machine is known which is able to bend a long sheet by using a punch which is equipped with a cam mechanism and has an inclined shape. This machine needs also a plurality of punch guides 6 what turns the machine more complicate, less compact and less flexible. Furthermore, for each shape of butt-end bend to be made a special set of tools needs to be employed, ie. a special knife and a corresponding dihedron. This, of course, brings about considerable costs owing to both the number of tool sets needed and their replacement, or set-up, at each model change in production. It therefore would be desirable, and it is actually an object of the present invention, to provide a sheet-metal bending process which is able to eliminate all of the afore cited drawbacks and, in particular, to enable the length portion of the sheet-metal plate to be kept constantly on its horizontal plane , and which is reliable, cost-effective, easily implemented through the use of currently available techniques and equipment, as well as to provide a machine which is capable of performing said process. In order that the present invention may more readily be understood, the following description is given, merely by way of non-limiting example, reference being made to the accompanying drawings in which: Figure 1 is a schematical view of a machine according to the present invention in its starting position; Figures 2, 3, 4 and 5 are views showing four subsequent operating positions of the machine according to the present invention. The process according to the present invention is based essentially on the fact that the bending operation is performed in three distinct phases, wherein a blank-holder is lowered in the first phase, by means of an appropriate motor-driven piston, on to the plate to be bent so as to keep it firmly between said blank-holder and an appropriate anvil , wherein in the second phase the continuation of said downward displacement of the piston that caused the blank-holder to go down causes a knife to be pushed downward, the lower end of said knife abutting then against the sheet-metal plate to be bent and causing it to therefore rotate around an appropriate edge of said anvil so as to cause said plate to undergo a first 90°-bending, and wherein in the third phase the continued downward movement of said piston forces the rotation and the consequential lowering of said knife so that one of its ends presses on the bent side of the sheet-metal plate, thereby causing it to further bend around the corresponding inclined and re-entrant edge of the anvil, as this is apparent from the illustrations in the Figures and the following description of the machine. Referring now to the accompanying Figures, these are seen to illustrate a machine comprising following elements: 1 • Sheet-metal plate to be bent 1a • Edge portion of the plate bent by a 90°-angle 1b • Edge portion of the plate bent by a greater angle than 90° 2 • Anvil or dihedron 3 • Thrust generating and transmitting piston 4 • Blank-holder 5 • Spring transmitting pressure from piston 3 to blank holder 4 6 • Thrust pin acting on knife 11 7 • Head of said pin 6 8 • Abutment of the head 7 of the pin 6 against the lever 11a 9 • Travel path of the pin 6 10 • Rotation rod of knife 11 11 • Knife for bending edge portion 1a, 1b of plate 1 11a • Actuating lever for knife 11 12 • Lower operating end of knife 11 13 • Terminal bending tip of knife 11 14 • Spring contrasting rotation of knife 11 15 • Lower re-entrant edge of anvil 2. All these elements are interconnected and operate as follows: At the beginning of the process (Fig. 1), the sheet-metal plate 1 is laid upon the anvil 2. The blank-holder 4 and the piston 3 are separated by a free space of mutual displacement and are connected by a spring 5 and a pin 5a whose purpose, operation and peculiarities will be further explained later on. The body of the piston 3 is raised and, therefore, both the spring 5 of the blank-holder 4, arranged between said blank-holder and the piston 3, and the spring 14 contrasting the knife 11, arranged between the lever 11a of said knife and the piston 3, are extended, ie. relaxed, since they work as compression springs. The knife 11 and its actuation lever 11a are connected with the piston 3 through the rod 10 that is fixedly provided on said piston, said rod being the force transmitting element that actually causes said knife and said lever to rotate with respect to the piston 3. The thrust pin 6 , which is firmly associated with the blank-holder on its upper portion, lies at the bottom end of its stroke with respect to the piston 3, the blank-holder 4 lies in a raised position with respect to the sheet-metal plate 1, while the knife 11, which is at rest, lies in a substantially vertical position, rotated to its clockwise uttermost position, due to the action of the spring 14 that pushes the actuation lever 11a against an appropriate abutment (not shown) situated on the piston 3. The lower end 12 of said knife 11 is separated from the sheet-metal plate by a distance which is greater than the distance separating the same plate from the lower surface of the blank-holder 4. In the next phase of the process (Fig. 2), the thrust generating and transmitting piston 3 is lowered until the blank-holder 4 is enabled to come into contact with the sheet-metal plate 1. All of the remaining elements of the system keep on the other hand an unchanged position with respect to each other. By continuing its downward displacement (Fig. 3), said piston 3 completes a further downstroke by a length that is equal to the height difference "L" between the lower surface of the blank-holder 4 and the lower end 12 of the knife 11, thereby compressing the spring 5. In this phase of the process, the lower end 12 of the knife 11, which is actuated by the rod 10, goes down to come into contact with the protruding edge portion of the plate 1, however without exerting any pressure on it yet. Furthermore, the spring 14 between the lever 11a and the piston 3 is not compressed, since it is not being loaded yet, due to the head 7 of the pin 6 not having yet reached the abutment 8 located on the lower side of the lever 11a. In the following phase (Fig. 4), the thrust generating and transmitting piston 3, continuing in its downward displacement, pushes through the rod 10 the knife 11 further downward, so that the lower end 12 of said knife 11 is now able to push, and bend by a 90°-angle in an anti-clockwise direction, the edge portion 1a of the sheet-metal plate protruding from the anvil 2. The further downward displacement of the piston 3, as it continues its downward stroke even after the blank-holder has come down onto the sheet-metal plate and the lower end 12 of the knife 11 has come down onto the protruding edge portion of the sheet-metal plate 1, is enabled by the fact that there is a free travel space between said piston and said blank-holder, said space being partially used by the pressure transmitting spring 5, said pressure transmitting spring 5 being guided by the coaxial pin 5a and the pin 6. The downstroke of the thrust generating and transmitting piston 3 continues (Fig. 5) down to the point at which the pin 6, which is rigidly associated with the blank-holder 4, strikes with its head 7 against the abutment 8; from this point on, the further downward movement of the piston 3 causes the head 7 of the pin 6 to accordingly push against said abutment 8 and this, in turn, causes the lever 11a to be pushed upward, so that the latter, which is journalled on the rod 10 attached to the piston 3, acts in turn to cause in this way the knife 11, and in particular its terminal tip 13, to rotate in an anti-clockwise direction. Being already in contact with the edge portion 1a of the plate which has just been bent at right angle, said terminal tip of the knife imparts an anti-clockwise rotary thrust to the same edge portion in such a way that said edge portion (1b) of the plate undergoes further bending about the edge of the anvil toward the reentrant inclined edge 15, however without touching the latter, and takes therefore the desired inclination which, apart from the sizing of the various afore described components, will also depend on the particular sequencing of the various actuators and movements of the machine, as made possible by the numerical-control technology. Once this last process phase is completed, the machine is restored in its initial starting condition shown in Fig. 1 by simply raising the piston 3 so that the latter will move with it the various afore cited operating elements of the machine by performing automatically, in a reverse sequence, the various afore illustrated movements until the initial positions of said elements are fully recovered owing also to the action of the springs 5 and 14. This process, in conjunction with the described machine, enable following further advantages to be achieved: simpler bending process, shorter bending times, use of a single anvil for a greater number of inclination or bending angles, easier programming of the whole machine by using the possibilities offered in this connection by the numerical-control technology, simpler and easier implementation of the process, greater operational safety and reliability. Anyone skilled in the art will now be in a position as to appreciate that this last operation sequence to reset the machine can be easily integrated with the afore described sequences, by simply programming in a suitable way, as anyone skilled in the art is certainly able to do, the control and actuation system of the machine. It will be further apparent that the above illustrated process and machine may be the subject of any modification and/or addition to accomodate any of a number of construction and/or operation variants that may be considered to be appropriate, such as for instance a construction geometry that is the inverse of the one being shown and illustrated here, or the use of springs that operate in an extension mode rather than in a compression one and that are appropriately relocated, or even an inverted arrangement of the pin 6 which may therefore be attached to the lever 11a and operated to act on the blank-holder 4, instead of the opposite arrangement described and illustrated here by way of example.

Claims: Bending machine for bending a plate of press-formable material, comprising a blank-holder means (4) to firmly hold the plate (1) on the horizontal plane between said blank-holder means and an appropriate anvil (2), and a knife-shaped tool (11) to perform the bending operation, said tool (11) being able to perform a first bending phase through a purely translational movement and a second bending phase through a combined translational-rotational movement, where in said first bending phase the edge portion of the plate is bent by a 90° angle and in said second bending phase the bending angle is increased to any greater angle than 90°, and comprising an actuation piston (3) which is connected to said blank-holder means (4) by a further pin (5a) which only allows said piston (3) to move perpendicularly to said blank-holder means, characterized in that : the knife-shaped tool (11) is rigidly connected to an actuating lever (11a) rotating on a rod (10) whose position is fixed w.r.t. said actuation piston(3), said lever (11a) extends into a gap between said piston and said blank-holder means (4), said lever is actuated by engagement of the head of a pin (6) mounted on the blank-holder means or lever, with the other of said blank-holder means or lever. Bending machine according to claim 1, characterized in that a first spring (5) is provided to keep elastically separated the piston (3) from the blank-holder means (4) and a second spring (14) is provided to keep elastically separated the piston (3) from the portion of the lever opposite to the connection part of said knife shaped tool. Bending machine according to any one of the preceding claims, characterized in that said knife-shaped tool (11) is provided with a bottom face (12) which is substantially flat, and its termination (13) oriented towards said blank-holder means shows an acute angle. Bending machine according to claim 3, characterized in that the distance between the bottom face (12) and the plate (1) is less than the distance between the corresponding contact points on the head (7) of said pin (6) and the abutment (8) of said lever (11a), when said actuating piston (3) is at the highest possible position.

Inventors: DE NARDI IRENEO, DE NARDI, IRENEO
Applicants: SIPA PROGETTAZIONE AUTOMAZ, S.I.P.A. SOCIETA INDUSTRIALIZZAZIONE PROGETTAZIONE E AUTOMAZIONE - S.P.A.
Application year: 1994
Main classification: B21D5
IPC codes: B21D5